1. Field of the Invention
The present invention relates to a pipeline excess flow valve (EFV) and its retrofitting with compatible installation equipment into an existing gas service line.
2. Prior Art
Conventional combustible gas distribution systems bring gas from a street main below ground level, through a tapping tee, a service line, a riser above ground level, a meter cock, a regulator, a meter and then into the customer's structure. An example of such system is shown in FIG. 1.
Rupture of the line or failure of fittings between the consumer property line and the served customer structure can occur for any number of reasons. Among these are digging by the customer or other party, vehicular impact, ground settling, failure of a regulator, failure of a meter, failure of fittings and earthquakes. Rupture of the line or failure of fittings can also occur on the inside customer fuel gas piping or flexible connection. Dangerous explosive conditions can arise when any such rupture occurs.
Prior art patents show various structures for shutting off the gas flow when the flow exceeds a predetermined value, e.g. due to the downstream rupture. Excess flow valves are used in the natural gas industry to prevent explosive pipeline gases such as natural gas, propane, methane, coal gas, town gas, etc. from escaping when a pipe is ruptured. These safety valves will remain open during normal use, when there is backpressure downstream from the valve, but will trip (snap shut) when the downstream pressure disappears. This prevents fires and explosions when gas lines are ruptured.
In operation, the stem of a conventional EFV such as that shown in U.S. Pat. No. 5,551,476 is spring biased opposite to the direction of gas flow. Under normal conditions the poppet on the stem is held away from a valve seat by the bias spring. When the flow is excessive such as when the service line ruptures downstream of the EFV, the forces from the flowing fluid overcome the spring bias and the poppet closes against the seat, shutting off the flow. Thus, the dangerous flow of combustible gas is stopped.
Presently, in order to install an EFV in an existing service line a hole or trench must be dug, the service line pressure must be reduced to zero, and the service line must be cut. This is not only expensive, time consuming, and disruptive to customers and traffic flows, it is also impractical in terms of the human resources required.
The main technology barriers to retrofitting EFVs without digging have been the actual anchoring of the device in the service line. The anchoring of the device has been an issue since it is unacceptable to damage or otherwise alter the interior wall of the service piping. The method of insertion has been an issue because the valves and fittings attached to the meter set have unpredictable geometry and the bend in the service riser presents a constraint in terms of the length of the EFV and the rigidity of the installation tool.